Stimulation, or hydraulic fracturing, of an onshore reservoir is used to increase production from the reservoir. The operation involves pumping a fracturing fluid at high pressure down a wellbore extending into the reservoir. The fluid puts pressure on the formation surrounding the wellbore, causing the formation to fracture.
The most common pad-fracturing operation deployed today uses plug-and-perf zipper methods, where two or more wells on a well pad are stimulated in a specific sequence to reduce downtime between frac stages and wireline trips. In this operation, one well is stimulated while simultaneously tripping into a nearby well on the pad with wireline to plug and isolate previously stimulated frac stages and perforate a new frac stage to be stimulated.
Perforated frac stages consist of multiple perforation clusters (usually 4-12 clusters per stage), wherein each perforation cluster is designed to be a primary hydraulic fracture from the wellbore into the reservoir. Due to a variety of factors, poor distribution of fluid and proppant across the clusters within a frac stage is highly probable. Near wellbore diverters are used to reduce the degree of poor fluid and proppant distribution. While diverters usually improve fluid and proppant distribution, this improvement is mostly marginal due to lack knowledge of how many perforations are taking fluid at any given time during the stimulation. In some cases, diverters can worsen distribution profiles.
Pinpoint methods are used to provide a more even distribution of fluid and proppant along the wellbore, as compared to multi-cluster plug-and-pert methods, because each fracture is generated sequentially in time. Most proven pinpoint methods require rigging coiled tubing or jointed tubing in-hole while stimulating the well. These methods are considered to constitute higher risk operations, compared to plug-and-perf operations. The use of rigging in-hole methods also limits pad stimulation efficiencies. Moreover, coiled tubing has limitations in terms of reaching extended wells.
There are pinpoint methods that do not require the use of tubing in-hole. In these methods, sleeves are permanently installed with the production liner or casing. Balls or collets are used to shift the sleeves open for stimulation one at a time and to isolate previously stimulated sleeves.
For the majority of multi-well pads (i.e., more than 98%), permanent wellbore construction tools are used, including perforation clusters and/or sleeve systems installed into the host casing. The most common completion method used today is the plug-and-perf (stimulation per set of perforation clusters), which is considered very efficient for stimulating a pad of wells when the zipper technique is possible. However, a poor stimulation distribution within the reservoir is obtained and it requires workover to remove the plugs that were installed to isolate the stages. In contrast, pinpoint systems constitute a more controlled completion method for efficient stimulation operations for a single well, with an even stimulation distribution within the reservoir. But the constraint is that the capital expenditure is greater compared to plug-and-perf methods for a pad of wells.
In addition, most of these pinpoint systems available in the market consists of permanently installed sleeves which are not suitable or may not be reliable for future secondary recovery methods or for future re-stimulation. Permanent sleeves are expensive and only function during the stimulation portion of the well's life (e.g. days to stimulate versus 40 years of productive life). Additionally, the sleeves are exposed to the reservoir and well environment, compromising their functionality for future stimulation applications.